Pyrazolo(1,5-a)benzimidazole couplers

ABSTRACT

The invention provides a method for the production of a pyrazolo(1,5-a)benzimidazole of the general formula (A): ##STR1## wherein R is a substituted or unsubstituted alkyl or aryl group, and 
     R 1  -R 4  =R, H, halogen, OR, COOR, CONHR, SO 2 , NO 2  NHR, NR 2 , or CN, and 
     X is hydogen or a reactive group releasable on coupling with an oxidized color developer, wherein the invention provides reacting a 2-amino or 2-mercapto substituted benzimidazole to form a triazepinone or a thiadiazino derivative respectively, ring contracting said triazepinone or thiadiazino derivative to give the corresponding 2-methylpyrazolobenzimidazole product, and subsequently removing the substituents at the -3 or -4 positions to provide a compound of the general formula (1).

DESCRIPTION

The present invention relates to pyrazolo(1,5-a)benzimidazole couplers.

The pyrazolo(1,5-a)benzimidazole (PBI) couplers are useful as magentacouplers for colour photography.

Although previous synthetic routes for the production of these compoundsare known the present invention provides a method for their productionusing ring closure reactions of benzimidazole derivatives.

According to the present invention there is provided a method for theproduction of a pyrazolo(1,5-a)benzimidazole of the general formula (A):##STR2## wherein R is a substituted or unsubstituted alkyl or arylgroup, and

R¹ -R⁴ =R, H, halogen, OR, COOR, CONHR, SO₂, NO₂ NHR, NR₂, or CN, and

X is hydrogen or a group releasable on coupling with an oxidised colourdeveloper, which method is characterised by reacting a 2-amino or2-mercapto substituted benzimidazole to form a triazepinone or athiadiazino derivative respectively, ring contracting said triazepinoneor thiadiazino derivative to give the correspondingpyrazolobenzimidazole product, and subsequently removing thesubstituents at the -3 or -4 positions to provide a compound of thegeneral formula (A).

In a preferred form of the invention R is a methyl or phenyl group andR¹ to R⁴ are all H. In another form of the invention R, R² and R³ areall methyl with R¹ and R⁴ respectively being a hydrogen substituent.

In one preferred form of the invention the 2-aminobenzimidazole startingmaterial is formed into a 1,2-4-triazepinone derivative and subsequentlysubjected to ring contraction of the 7-member ring to the pyrazole form.

In another form of the invention a thiadiazinobenzimidazole derivativeis subjected to a ring contraction of the 6-member ring to give thepyrazole form.

Accordingly the alkyl or aryl pyrazolo(1,5-a)benzimidazole derivativesof the present invention may be formed either by means of the mercaptocompound (referred to hereinafter as the sulphur extrusion route), or bymeans of the amino substituted compound (hereinafter referred to as thering contraction route).

In one generally exemplary exposition of the sulphur extrusion route thestarting materials are selected from a 2-mercaptobenzimidazole and anα-haloketone.

The former compounds are readily available from ortho-phenylene diaminesand carbon disulphide.

Accordingly 2-methylpyrazolo(1,5-a)benzimidazole may be produced byreacting 2-mercaptobenzimidazole (1) with a haloketone such aschloroacetone at the sulphur atom to give a corresponding substitutedketone (2). A plurality of different α-haloketones may be utilized inthis reaction depending upon the desired product or reaction conditions.

Thus where a 2-mercaptobenzimidazole is utilized the substituted ketonestarting material may be 2-(acetylmethylthio)benzimidazole. If this lastproduct is reacted under alkaline aqueous conditions with hydroxylamineO-sulphonic acid, at for example, room temperature it gives aprecipitate of a thiadiazinobenzimidazole derivative (4) in high yield.This last reaction is believed to proceed via the N-amination of the2-(acetylmethylthio)benzimidazole to give an intermediate productdesignated (3) which rapidly cyclises with a loss of water to give thedesired compound.

The six membered ring including the sulphur atom may be ring contractedby heating with a mixture of acetic acid and toluene for a number ofhours; for example 80. The product which may be4-acetyl-3-acetylthio-2-methylpyrazolo(1,5-a)-benzimidazole (5) may thenbe desulphurised under reflux in the presence of mineral acid andethanol to give the desired 2-methylpyrazolobenzimidazole product.

This reaction sequence is shown diagrammatically in scheme 1 below.##STR3##

The mechanism of the ring contraction of scheme 1 has not yet been fullyelucidated. It is thought probable that a mechanism somewhat as shown inscheme 2 below is involved. Without limitation it is believed that thearrangement shown in scheme 2 involves the initial acylation of theimidazole nitrogen followed by ring formation and subsequent cleavage,possibly assisted by the generation of an acetate anion. A similarmechanism could exist whereby the sulphur atom is initially acylated;the penultimate structure is common to both mechanisms. ##STR4##

The particular advantages of this route, are that clean, high yieldingsteps provide the target compound; starting from starting materialswhich are readily available.

In the ring contraction route alluded to above, a seven membered1,2,4-triazepinone derivative of the pyrazole ring of the coupler ismade by heating in the absence or in the presence of acetic anhydride.Starting materials for the production of PBI by this route may include2-amino-benzimidazole. This compound is readily available from a numberof sources usually via ortho-phenylenediamine or a 2-H-benzimidazole. Ifthe 2-methyl derivative is to be the final product, 2-aminobenzimidazolemay be the starting material. In this case the starting material may bereacted in alkaline solution with hydroxylamine O-sulphonic acid to givea 1,2-diaminobenzimidazole intermediate. This intermediate may bereacted with alkyl acetoacetate in an organic solvent, for examplexylene containing acetic acid, to give a 1,2,4-triazepinone derivative.This seven-membered ring structure may be ring contracted by reflux, inthe presence of acetic anhydride for example, to afford two products inapproximate equal quantities; the first being a diacetyltriazepinone andthe second being N-acetyl-2-methylpyrazolobenzimidazole. Reflux in thepresence of acidified alcohol removes the acetyl component to providethe target compound.

This reaction sequence is demonstrated diagrammatically in scheme 3below. ##STR5##

Although the mechanism of the ring contraction step has yet to be fullyelucidated, and we do not wish to be held to any precise theory thereof,the pathway seems to be the same as for the sulphur extrusion method. Inthis case the intramolecular cyclisation occurs to give a four ratherthan a three membered ring with subsequent loss of an isocyanate anion.##STR6##

This last route has also been applied to the synthesis of2,6,7-trimethylpyrazolo(1,5-a)benzimidazole from4,5-dimethyl-benzimidazole. This product has been more difficult toproduce because of the difficulties of providing suitable startingmaterials in the prior art.

In order to provide this last compound the 4,5-dimethylbenzimidazole wasN-aminated to give a 91% crude product which gave an 81% yield of thecorresponding triazepinone with an alkyl acetoacetate. This product wasthen refluxed with acetic anhydride to give the same mixture ofproducts, one corresponding to the diacetyl derivative of thetriazepinone (12%) yield and the other to give N-acetyl PBI at 54%yield; hydrolysis of the latter with hydrochloric acid in an alcoholsuch as ethanol gave free PBI at 98% yield.

The ring contraction route in accordance with the present invention isuseful in the preparation of novel PBIs with substituents in the benzoring which are normally difficult to prepare.

By analogous methods the 2-methylpyrazolo-(1,5-a)-dimethylbenzimidazoleand the 2-phenylpyrazolo (1,5-a)benzimidazole derivatives shown can beobtained. ##STR7##

The dye-forming couplers of this invention can be used in the ways andfor the purposes that dye-forming couplers have been previously used inthe photographic art. They may be dissolved in processing solutions(unballasted) or incorporated into photographic materials (normallyballasted).

Typically, the couplers are incorporated in silver halide emulsions andthe emulsions coated on a support to form a photographic element.Alternatively, the couplers can be incorporated in photographic elementsadjacent the silver halide emulsion where, during development, thecoupler will be in reactive association with development products suchas oxidized colour developing agent. Thus, as used herein, the term"associated therewith" signifies that the coupler is in the silverhalide emulsion layer or in an adjacent location where, duringprocessing, it will come into reactive association with silver halidedevelopment products.

The photographic elements can be single colour elements or multicolourelements. In a multicolour element, the magenta dye-forming couplers ofthis invention would usually be associated with a green-sensitiveemulsion, although they could be associated with an emulsion sensitizedto a different region of the spectrum, or with a panchromaticallysensitized orthochromatically sensitized or unsensitized emulsion.Multicolour elements contain dye image-forming units sensitive to eachof the three primary regions of the spectrum. Each unit can be comprisedof a single emulsion layer or of multiple emulsion layers sensitive to agiven region of the spectrum. The layers of the element, including thelayers of the image-forming units, can be arranged in various orders asknown in the art.

A typical multicolour photographic element would comprise a supportbearing a magenta dye image-forming unit comprised of at least onegreen-sensitive silver halide emulsion layer having associated therewithat least one magenta dye-forming coupler, at least one of the magentadye-forming couplers being a coupler of this invention, and yellow andcyan dye image-forming units comprising at least one blue- orred-sensitive silver halide emulsion layer having associated therewithat least one yellow or cyan dye-forming coupler respectively. Theelement can contain additional layers, such as filter layers.

In the following discussion of suitable materials for use in theemulsions and elements of this invention, reference will be made toResearch Disclosure, December 1978, Item 17643, published by IndustrialOpportunities Ltd., The Old Harbourmaster's, 8 North Street, Emsworth,Hants P010 7DD, U.K. This publication will be identified hereafter as"Research Disclosure".

The silver halide emulsion employed in the elements of this inventioncan be either negative-working or positive-working. Suitable emulsionsand their preparations are described in Research Disclosure Sections Iand II and the publications cited therein. Suitable vehicles for theemulsion layers and other layers of elements of this invention aredescribed in Research Disclosure Section IX and the publications citedtherein.

In addition to the couplers of this invention, the elements of theinvention can include additional couplers as described in ResearchDisclosure Section VII, paragraphs D, E, F and G and the publicationscited therein. The couplers of this invention and any additionalcouplers can be incorporated in the elements and emulsions as describedin Research Disclosures of Section VII, paragraph C and the publicationscited therein.

The photographic elements of this invention or individual layersthereof, can contain brighteners (see Research Disclosure Section V),antifoggants and stabilizers (see Research Disclosure Section VI),antistain agents and image dye stabilizer (see Research DisclosureSection VII, paragraphs I and J), light absorbing and scatteringmaterials (see Research Disclosure Section VIII), hardeners (seeResearch Disclosure Section XI), plasticizers and lubricants (seeResearch Disclosure Section XII), antistatic agents (see ResearchDisclosure Section XIII), matting agents (see Research DisclosureSection XVI) and development modifiers (see Research Disclosure SectionXXI).

The photographic elements can be coated on a variety of supports asdescribed in Research Disclosure Section XVII and the referencesdescribed therein.

Photographic elements can be exposed to actinic radiation, typically inthe visible region of the spectrum, to form a latent image as describedin Research Disclosure Section XVIII and then processed to form avisible dye image as described in Research Disclosure Section XIX.Processing to form a visible dye image includes the step of contactingthe element with a colour developing agent to reduce developable silverhalide and oxidize the colour developing agent. Oxidized colourdeveloping agent in turn reacts with the coupler to yield a dye.

Preferred colour developing agents are p-phenylene diamines. Especiallypreferred are 4-amino-N,N-diethylaniline hydrochloride,4-amino-3-methyl-N-ethyl-N-β-(methanesulfonamideo)ethylaniline sulphatehydrate, 4-amino-3-methyl-N-ethyl-N-β-hydroxyethylaniline sulphate,4-amino-3-β-(methanesulfonamido)ethyl-N,N-diethylaniline hydrochlorideand 4-amino-N-ethyl-N-(2-methoxyethyl)-m-toluidine di-p-toluenesulfonate.

With negative-working silver halide emulsions this processing step leadsto a negative image. To obtain a positive (or reversal) image, this stepcan be preceded by development with a non-chromogenic developing agentto develop exposed silver halide, but not form dye, and then uniformfogging of the element to render unexposed silver halide developable.Alternatively a direct positive emulsion can be employed to obtain apositive image.

Development is followed by the conventional steps of bleaching, fixingor bleach-fixing, to remove silver and silver halide, washing anddrying.

The invention will now be described, by way of illustration only in thefollowing examples of the invention.

EXAMPLE 1 a) The Sulphur Extrusion Route Preparation of2-(Acetylmethylthio)benzimidazole (2)

2-Mercaptobenzimidazole (14.6 g, 0.1 mole) and chloroacetone (9.25 g,0.1 mole) were added to 2-butanone (400 ml) and refluxed for 5 hrs. Oncooling the product hydrochloride, 21.24 g, 88% was isolated byfiltration, washed with acetone and air dried. The salt was dissolved inwater (150 ml) and added to a solution of sodium acetate (7.2 g, 0.088mole) in water (100 ml). The oil obtained was extracted into ethylacetate, filtered to remove some insoluble material (0.4 g), dried andevaporated to dryness. The residue was crystallised from ethanol to givethree crops of 2-(acetylmethylthio)benzimidazole (2), as colourlesscrystals, 15.0 g, 73%, mp. 112°-113° C. PMR was consistent with atautomeric mixture of the open chain and ring closed forms.

C₁₀ H₁₀ N₂ OS Requires: C 58.2%, H 4.9%, N 13.6%, S 15.5%. Found: C58.4%, H 5.2%, N 13.6%, S 14.5%.

(b) Preparation of 2,2-H-3-Methyl-1,3,4-thiadiazino[3,2-a]benzimidazole(3).

2-(Acetylmethylthio)benzimidazole (10.3 g, 50 mmole) was dissolved in asolution of potassium hydroxide (6.5 g, 115 mmole) in water (125 ml) andhydroxylamine O-sulphonic acid (tech. 6.2 g, 55 mmole) added in oneportion with stirring at ambient temperature. The reagent dissolvedimmediately and after a few minutes a white precipitate was obtained.The mixture was stirred for 30 minutes and the product filtered off,washed and dried, 9.6 g, 95%. This was essentially one component by TLC(2:1 ethyl acetate:petrol). A sample was recrystallised from aqueousethanol for characterisation, mp. 144°-146° C. Spectroscopic data wasconsistent for (3).

C₁₀ H₉ N₃ S Requires: C 59.1%, H 4.5%, N 20.7%, S 15.8%. Found: C 59.1%,H 4.7%, N 20.5%, S 15.5%.

(c) Preparation of4-Acetyl-3-acetylthio-2-methylpyrazolo[1,5-a]benzimidazole (5)

2,2-H-3-Methyl-1,3,4-thiadiazino[3,2-a]benzimidazole (2.0 g, 10 mmole)was added to a mixture of toluene (20 ml) and acetic anhydride (5 ml)and heated to reflux for 24 hr. After 6 hr TLC (ethyl acetate) indicatedapproximately 40-50% conversion to a single product which onlymarginally increased with time. A further aliquot of acetic anhydride (5ml) was added and heating continued for a total 80 hrs (followed byTLC). After this time TLC indicated a 80-90% conversion and a beigesolid began to crystallise from the mixture. On cooling the mass ofcrystals were filtered off, washed with a little acetic acid and airdried, 2.6 g, 91%, mp. 191°-193° C. Spectroscopic data was consistentwith (5).

C₁₄ H₁₃ N₃ O₂ S Requires: C 58.5%, H 4.6%, N 14.6%, S 11.2%. Found: C58.5%, H 4.7%, N 14.5%, S 11.3%.

(d) Preparation of 2-Methylpyrazolo[1,5-a]benzimidazole (6).

4-Acetyl-3-acetylthio-2-methylpyrazolo[1,5-a]benzimidazole (2.0 g, 6.97mmole) was added to a mixture of concentrated hydrochloric acid (5 ml)and ethanol (30 ml) and refluxed for 5 hr. A yellow solid precipitatedduring the heating period and was filtered off after cooling, 0.9 g.This was a mixture of several components, none of them being therequired product, and was discarded. The ethanolic solution was pouredinto a solution of sodium bicarbonate (excess) in water (300 ml) and thewhite solid filtered off, washed and dried, 0.7 g, 61%, mp. 250°-252° C.IR and TLC (+ Dox spray test) comparison with authentic (6) showed thesamples to be identical.

EXAMPLE 2 The Ring Contraction Route (a) Preparation of1,2-Diaminobenzimidazole (8).

Hydroxylamine O-sulphonic acid (tech. 23.25 g, 205 mmol) was added to astirred solution of 2-aminobenzimidazole (25 g, 187.5 mmol) dissolved inwater (600 ml) containing potassium hydroxide (24.6 g, 438 mmol) at 23°C. After a few moments a white solid began to precipitate. The mixturewas stirred for 30 mins and the product collected by filtration, washedwith water and dried in air at ambient temperature, 10.75 g. On standingovernight a second crop, 5.8 g was obtained. The total yield of productwas 16.55 g, 60%, mp. 252°-254° C., (lit. 255°-259° C.). Spectroscopicanalysis was consistent with the product but indicated a small amount ofthe starting material was also present. This was used without furtherpurification (note 1).

C₇ H₈ N₄ Requires: C 56.7%, H 5.4%, N 37.8%. Found: C 58.1%, H 5.4%, N36.5%.

(b) Preparation of3H-2-Methyl-1,2,4-triazepino[2,3-a]benzimidazole-4(5H)-one (9)

1,2-Diaminobenzimidazole (3.0 g, 20 mmol) was added to a mixture ofxylene (25 ml), ethyl acetoacetate (5.2 g, 40 mmol) and acetic acid (1.5ml) and heated at 110° C. for 2 hr and then refluxed for a further 1 hr.After cooling to room temperature the precipitate was filtered offwashed with toluene and dried in air to give pure (9), 2.5 g, 58%.Spectroscopic analysis was consistent with the product.

C₁₁ H₁₀ N₄ O Requires: C 61.7%, H 4.7%, N 26.15%. Found: C 61.5%, H4.8%, N 26.1%.

c) Reaction of Triazepinone (9) with Acetic Anhydride

Triazepinone (9) (1.0 g, 4.67 mmol) was added to acetic anhydride (5 ml)and heated at reflux. The reaction was followed by thin layerchromatography, (1:1 ethyl acetate: 60°-80° C. petroleum ether), andindicated that two products (Rf=0.1 and 0.8, SM=0.15) were being formed.After heating for 4 hr the reaction was complete and the solution wasallowed to cool to room temperature overnight. The mass of fine needlesthat were formed were filtered off, washed with a little acetic acid anddried in air, 0.65 g. Recrystallisation from acetic acid gave a puresample of product 1, (Rf=0.8), identified as5-H-2-Methyl-3-acetyl-4-acetoxy-1,2,4-triazepino[2,3-a]benzimidazole(10), mp. 218°-220° C. The yield of product 1 was 0.65 g, 47%.

Product 1; C₁₅ H₁₄ N₄ O₃ Requires: C 60.4%, H 4.7%, N 18.8%. Found: C59.9%, H 4.8%, N 18.5%.

The reaction filtrate, containing product 2, was poured into stirredwater (75 ml) and the buff solid isolated by filtration, washed withwater and dried in air. This was shown, by spectroscopic analysis, to bealmost pure 2-methyl-4-acetylpyrazolo[1,5-a]benzimidazole (11), mp.158°-160° C., 0.3 g, 35%.

Product 2; C₁₂ H₁₁ N₃ O Requires: C 67.6%, H 5.2%, N 19.7% Found: C66.9%, H 5.2%, N 19.6%

(d) Preparation of 2-methylpyrazolo[1,5-a]benzimidazole (6)

2-Methyl-4-acetylpyrazolo[1,5-a]benzimidazole (11), (0.25 g, 1.17 mmol),was added to a mixture of concentrated hydrochloric acid (0.5 ml) inethanol (5 ml) and heated to reflux for 20 minutes. The solution wascooled to room temperature and poured into a solution of sodiumbicarbonate in water (30 ml) to afford a light tan solid which wasfiltered off, washed and dried, mp. 248°-252° C., 0.20 g, 99%. This wasshown by comparative thin layer chromatography and infra-red analysis tobe identical to an authentic sample of2-methylpyrazolo-[1,5-a]benzimidazole (6).

EXAMPLE 3

The couplers described above were converted by conventional methods tothe following ballasted couplers for photographic evaluation in an E6process (well known development process for colour reversal processinge.g. Ektachrome). ##STR8##

The couplers were incorporated into a photographic silver bromoiodideemulsion and coated in the following format:

    ______________________________________                                        Gel Supercoat                                                                              Gelatin        1.5 gm-2                                          Emulsion     Silver bromoiodide                                                                           1.6 gm-2                                          Layer        Coupler        1.04 mmolm-2                                                   Gelatin        2.42 gm-2                                                      Bis(vinylsulphonyl)-                                                                         0.06 gm-2                                                      methane (hardener)                                               Support      Cellulose Acetate                                                ______________________________________                                    

The couplers dispersion used contained 6% w/w gelatin, 0.8% coupler andcoupler solvents in the ratio coupler:triphenylphosphate:2-(2-butoxyethoxy)ethyl acetate 1.0:0.5:1.5.

Strips of the coated material were fogged through a step wedge andprocessed in a standard E6 process. Sensitometry was carried out on thestrips to provide dye density curves from which Dmax and contrast(gamma) were measured. The dye hues (Lambda max) and half band width(HBW) were also measured.

    ______________________________________                                        Photographic Data                                                                                               Lambda                                      Coupler  Dmax     Dmin     Gamma  Max    HBW                                  ______________________________________                                        (1)      3.20     0.14     -3.18  571    118                                  (2)      0.61     0.13     --     580    112                                  (3)      0.28     0.10     --     550    110                                  (4)      1.09     0.10     -0.58  569    112                                  (5) Control)                                                                           1.46     0.09     -1.14  549     92                                  ______________________________________                                    

I claim:
 1. A method for the production of a pyrazolo (1,5-a)benzimidazole of the formula (A): ##STR9## wherein R is an alkyl or arylgroup;R¹ -R⁴ individually are R, H, halogen, or, COOR, CONHR, SO₂, NO₂,NHR, NR₂, or CN; and, X is hydrogen or a group releasable on couplingwith an oxidized color photographic developer, wherein the methodcomprises reacting a 2-amino or 2-mercapto substituted benzimidazole toform a triazepinone or a thiadiazino derivative respectively, ringcontracting said triazepinone or thiadiazino derivative to give thecorresponding 2-methylpyrazolobenzimidazole product, and subsequentlyremoving the substituents at the -3 or -4 positions to provide acompound of the formula (A).
 2. A method according to claim 1characterized in that R is methyl or phenyl and R¹ to R⁴ are H.
 3. Amethod according to claim 1 wherein R, R² and R³ are methyl and R¹ andR⁴ are hydrogen.
 4. A method according to claim 1 wherein the2-aminobenzimidazole is formed into a 1,2,4-triazepinone derivativebeing subsequently subjected to ring contracting of the sever-memberring to the pyrazole form.
 5. A method according to claim 1 wherein thethiadiazinobenzimidazole derivative is subjected to ring contraction ofthe six-member ring to give the pyrazole form.